Apparatus and method for reading and analyzing ECG images

ABSTRACT

A method of analyzing an electrocardiogram (ECG) paper chart includes the steps of scanning the ECG chart, to thereby create a computer-readable ECG image file representative of the ECG chart, storing the ECG image file in a memory of a computer, opening the ECG image file and displaying on a computer display an ECG plot corresponding to the ECG image file, calibrating the x-axis and y-axis of the displayed ECG plot with an x-axis scale and a y-axis scale, identifying characteristics of the ECG plot by using an input device connected to the computer, and measuring the identified characteristics.

FIELD OF THE INVENTION

The present invention relates generally to cardiology, and, moreparticularly, to an apparatus and method for reading and analyzingelectrocardiographic charts, especially electrocardiographic chartsrecorded on paper.

BACKGROUND OF THE INVENTION

Electrocardiograph (EKG) machines are used as a diagnostic tool inmedicine, and measure electrical activity in the heart muscle. Aftereach contraction of the heart, an electrical impulse is generated in thesinoatrial node (SA Node) of the heart. The EKG machine traces the pathof the impulse as it spreads though the heart, and produces a graph ortrace of the electrical impulses often referred to as anelectrocardiogram (ECG). There is a growing need to identify changesthat occur in ECGs that are associated with, for example,pharmacological interventions, genotypes and differentpathophysiological substrates. For example, one specific need is todetermine whether a given compound significantly modulates therepolarization duration process of cardiac beats.

Generally, EKG machines include or are associated with a printing meansthat produces on paper an ECG chart. Reading and analyzing the paper ECGchart typically requires the use of a ruler or a system of calipers inorder to measure and determine certain characteristics of the ECG, suchas, for example, time intervals and peak magnitudes. One example of sucha caliper system for use in measuring paper ECG charts is described inU.S. Pat. No. 4,388,759, which is herein incorporated by reference. Thecaliper system described therein is used to determine deflectionamplitudes, intervals and frequencies from standard ECG tracings orcharts, and consists of two calibrated caliper arms coupled together forrotation about a pivot pin to determine distances between differentcaliper points. A second example of a caliper system for use inmeasuring paper ECG charts is described in U.S. Pat. No. 4,936,022,which is also herein incorporated by reference. The caliper systemdescribed therein includes a multi-leg caliper device having a pluralityof parallel members and pivot points, and is used to measurecharacteristics of a conventional paper chart ECG by placing severalindicia over a suitably calibrated scale and comparing the values on theindicia chart adjacent indicating portions of the multi-leg caliper.

A problem arises when the desired measurement is a time duration betweentwo events. For example, one event may be a peak of one portion of awave and a valley of another portion. The peak and valley are separatedby a substantial vertical distance. An accurate measurement requiresprojecting the peak and the valley onto the horizontal time axis andthen measuring the time between the projected points. The projectionsmust be made to a common horizontal baseline and must be perpendicularthereto. If the baseline is angled from horizontal or if the projectionis other than perpendicular, errors in measurement are introduced.Mechanical methods for making such measurements are subject to human andmechanical error.

The above-described and other similar caliper systems are typicallyrestricted to reading only a few of the ECG characteristics of interest.Furthermore, such caliper systems are typically calibrated for use witha paper ECG chart having a predetermined resolution and/or scale, andthus can not be used with other paper charts having a differentresolution. Moreover, the caliper-based systems are manual andmechanical in nature, and are thus subject to poor reproducibility anderror. Varying resolutions and/or time scales of paper charts and thequality of the ECG tracing on the paper chart are just two examples offactors that have contributed to error and/or poor reproducibility inreading the paper ECG charts. These and other factors which negativelyimpact the reliability of manually reading paper ECG charts arediscussed in greater detail in Savelieva, I., et al., Agreement andReproducibility of Automatic versus Manual Measurement of QT Intervaland QT Dispersion, 81 Am. J. Cardiol. 471-477 (1998), and Murray, A., etal., Errors in Manual Measurement of QT Intervals, 71 Br. Heart J.,386-390 (1994), each of which are incorporated herein by reference.

Therefore, what is needed in the art is a method of reading andanalyzing an ECG chart that is less susceptible to error and has ahigher reproducibility.

Furthermore, what is needed in the art is a method of reading andanalyzing an ECG chart that is less mechanical in nature.

Still further, what is needed in the art is a method of reading andanalyzing an ECG chart that is capable of determining a substantialnumber of the electrocardiogram characteristics of interest.

Moreover, what is needed in the art is a method of reading and analyzingan ECG chart that is adaptable for use with charts having differentresolutions and/or scales.

SUMMARY OF THE INVENTION

The present invention provides an apparatus and method for analyzing anelectrocardiogram (ECG) paper chart.

The invention comprises, in one form thereof, a method of analyzing anelectrocardiogram (ECG) paper chart that includes the steps of scanningthe ECG chart, to thereby create a computer-readable ECG image filerepresentative of the ECG chart, storing the ECG image file in a memoryof a computer, opening the ECG image file and displaying on a computerdisplay an ECG plot corresponding to the ECG image file, calibrating thex-axis and y-axis of the displayed ECG plot with an x-axis scale and ay-axis scale, identifying characteristics of the ECG plot by using aninput device connected to the computer, and measuring an axialprojection of the identified characteristics by connecting a line at anyangle between the two points.

An advantage of the present invention is that reading and analyzing theECG chart is more automated.

Another advantage of the present invention is that a substantial numberof the electrocardiogram characteristics of interest are automaticallydetermined or determined with minimal user input.

Yet another advantage of the present invention is that error andreproducibility in reading and analyzing the ECG chart is reduced.

A still further advantage of the present invention is that it isadaptable for use with ECG charts having different resolutions and/orscales.

Other advantages of the present invention will be obvious to one skilledin the art and/or appear hereinafter.

BRIEF DESCRIPTION OF THE DRAWINGS

The above-mentioned and other features and advantages of this invention,and the manner of attaining them, will become appreciated and be morereadily understood by reference to the following detailed description ofone embodiment of the invention in conjunction with the accompanyingdrawings, wherein:

FIG. 1 is an illustrative ECG plot;

FIG. 2 shows one embodiment of an apparatus for reading and analyzing anECG chart of the present invention.

FIG. 3 is a flow chart illustrating one embodiment of a method forreading and analyzing an ECG chart of the present invention.

FIG. 4 is a bitmapped image of an ECG chart displayed in accordance withthe method of FIG. 3;

FIG. 5 is a display of a software-based toolbar for reading andanalyzing an ECG plot in accordance with the method of FIG. 3;

FIG. 6 shows a pop-up contextual menu for reading and analyzing an ECGplot in accordance with the method of FIG. 3;

FIG. 7 illustrates the step of identifying characteristics of an ECGplot in accordance with the method of FIG. 3;

FIG. 8 shows a software-based dialog box for use in the method ofreading and analyzing an ECG chart of FIG. 3; and

FIG. 9 is an example of an exported data file in accordance with themethod of reading and analyzing an ECG chart of FIG. 3.

Corresponding reference characters indicate corresponding partsthroughout the several views. The exemplification set out hereinillustrates one preferred embodiment of the invention, in one form, andsuch exemplification is not to be construed as limiting the scope of theinvention in any manner.

DETAILED DESCRIPTION OF THE DRAWINGS

The following terms as used herein are defined as follows. The phrase“reading an ECG” refers to obtaining values for and/or measuringparameters of an ECG. The term “QRS complex” refers to the largestfluctuation of the ECG signal of a duration of approximately 100milliseconds (mS). Lastly, the term “QT interval” refers to the timeinterval between the beginning of a QRS complex and the end of thefollowing T wave. The foregoing definitions are more particularlydescribed hereinafter, and will be more readily understood withreference to FIG. 1, wherein an illustrative ECG plot is shown.

Referring now to FIG. 1, ECG plot 10 includes two consecutive QRScomplexes, QRS 12 and QRS 14. QRS complex 12 is preceded by P wave 20,and includes a respective Q wave 22, R wave 24, and S wave 26. QRScomplex 12 is followed by T wave 28. Similarly, QRS complex 14 ispreceded by P wave 30, and includes a respective Q wave 32, R wave 34,and S wave 36. A respective T wave (not shown) follows QRS complex 14. Pwaves 20, 30 are due to the excitation of the atria. Q waves 22, 32, Rwaves 24, 34 and S waves 26, 36 result from the excitation of theventricles. T wave 28 is due to the ventricles returning to electricalsteady state (repolarization of the ventricles).

RR interval 40 is the time interval between R wave 24 and R wave 34, andprovides a direct estimate of instantaneous, rather than averaged, heartrate. QT interval 42 is the time interval between the onset of Q wave 22and end or offset of T wave 28, and it is useful in assessing the timebetween ventricular excitation (i.e., polarization and/or contraction)and ventricular return to steady state (i.e., repolarization and/ordecontraction).

Further of note in FIG. 1 are PR intervals 44, 46 and QRS intervals 52,54. PR intervals 44, 46 each reflect the time between a respectiveexcitation of the atria and excitation of the ventricles. QRS intervals52, 54 each reflect the time interval of a complete excitation of theventricular muscle.

At rest the heart is neutral and has a nominal zero voltage. However,normal ECGs have a wandering DC level. In other words, each cycle of thePQRST wave does not return to the same absolute value of zero.Nevertheless, the region of the wave following the T portion, and theregion between the P wave and following QRS wave, are consideredneutral, and sequential corresponding portions can be used to establisha baseline of zero volts. For purposes of illustration, assume that adoctor wanted to know the time between the R peak 24 of the first ECGand the Q valley 36 of the second one. Using prior art techniques, thetwo points would be projected onto a baseline Time as points 24I and 36Fand the distance between the two could be measured with a ruler.

In contrast, the invention allows the user to place a first end point ofa line L on the peak 24 and a second end point on the valley 36 tothereby measure the interval of interest. First, the horizontal axis isscaled. The scale is selected from data taken with the ECG. These areknown values of so many millivolts or seconds per division on the graphpaper. The scale for the x-axis is created by drawing a conventionalhorizontal line between two major divisions on the bit mapped image andentering the time represented by the distance. The y-axis is similarlyscaled. With the bitmapped imaged thus scaled, the computer programautomatically finds the length of the projection of the end points onthe respective horizontal and vertical axes. Since the image isbitmapped, the computer counts the horizontal and vertical pixelslocated between the two end points and displays the results. Thus, theangle of the line between the two points is determined. In order toprecisely place the end points of the line, the user may magnify or zoomin on the images and place the end points on the magnified peak orvalley. Of course, other methods of finding the axial projections couldbe used, including and not limited to solving the Pythagorean theoremand using trigonometry.

Referring now to FIG. 2, one embodiment of an apparatus for reading andanalyzing an ECG plot is shown. ECG analyzing and measurement system 60includes computer 62, such as, for example, a personal computer, andoptical scanner 64.

Personal computer 62 includes keyboard 66, mouse 68 and display 70.Personal computer 62 further includes application software 72, whichwill be more particularly described hereinafter, that is stored instorage device 74, such as, for example, a hard drive, floppy drive orcompact disk drive, connected to personal computer 62. Personal computer62 further includes read only memory (ROM) 76 and random access memory(RAM) 78. The basic functions of personal computer 62 are controlled byoperating system 80, such as, for example, a version of the WINDOWSoperating system.

Optical scanner 64 is electrically connected to computer 62, such as,for example, via an input/output port (not shown). Optical scanner 64 isa commercially available scanner such as those sold for use withpersonal computers as peripheral equipment.

Referring now to FIG. 3, the process steps of one embodiment of themethod of reading and analyzing an ECG of the present invention areshown. ECG reading and analyzing method 100 is performed by EGR readingsystem 60 running application software 72. As will be more particularlydescribed hereinafter, ECG reading and analyzing method 100 includesscanning step 102, file opening step 104, calibrating step 106, RRinterval identification step 108, QT interval identification step 110,PR/QRS interval identification step 112, display step 114, input step116 and exporting step 118.

Scanning step 102 of method 100 includes scanning ECG plot 10 withscanner 64. ECG plot 10 is placed on the scanning bed (not shown) ofoptical scanner 64. ECG plot 10 is a conventional plot with known scalesfor its horizontal and vertical axes. The image of the plot is typicallya light gray grid pattern that bears a dark line image of an ECG wave.Computer 62 controls the operation of scanner 64 through operatingsystem 80 or other software, and controls the execution of applicationsoftware 72 and, thus, method 100. Scanning step 102 creates image file82, and stores image file 82 as a computer-readable graphics file in RAM78 or storage device 74 of computer 62. After scanning, the bitmappedimage 82 comprises a plurality of pixels. All pixels are square and havethe same dimensions. Image file 82 is a graphics file of a predeterminedor user selected format, such as, for example, a bitmap file format or aJoint Photographic Experts Group (JPEG) file format. Scanning step 102scans ECG plot 10 at a resolution, such as, for example, approximately100 to 200 dots per inch (dpi), or higher, depending on the capabilitiesof scanner 64 and any user, software or apparatus-imposed limitations onfile size. Image file 82 is then opened and a representation thereofdisplayed on computer display 70 by file open step 104.

Referring now to FIG. 4, a representation of a scanned ECG wave isshown. Scanned ECG wave 120 is displayed on computer display 70, andincludes x-axis 120 x and y-axis 120 y. Scanned ECG wave 120 is theresult of scanning step 102, saving step 103 and file open step 104, andis a visual representation of image file 82. File open step 104 includesselecting and opening image file 82, and the display of image file 82 oncomputer display 70 as scanned ECG wave 120.

Calibration step 106 includes the addition by a user of a scale,typically time, for x-axis 120 x and a scale, typically voltage, fory-axis 120 y to scanned ECG wave 120. More particularly, and withreference to FIG. 5, calibration step 106 enables a user, through theuse of one or both of mouse 68 and keyboard 66, to access tool bar 130of application software 72 that is displayed on computer display 70 andincludes a plurality of buttons 132 a-132 q. Each of buttons 132 a-132 qincludes an icon (not referenced) representative of the functionsperformed by that button. By positioning mouse 68 upon an icon orbutton, or selecting the appropriate icon with the keys of keyboard 66,button 132 e is activated to enable the user to assign a scale or timeto x-axis 120 x, or button 132 f is activated to enable the user toassign a scale or voltage to y-axis 120 y of scanned ECG wave 120.

The toolbar 130 includes conventional Windows icons on buttons 132 a-cfor opening files, saving files and printing, respectively. Button 132 dselects and toggles the x-scale function and button 132 e confirms andlocks the scale. Button 132 f and 132 g perform corresponding functionsfor the y-axis. Buttons 132 h-l perform the functions of rotating theimage clockwise and counter-clockwise, and for enlarging, reducing anddoubling the size of the image, respectively. Button 132 m is used toselect a line that is drawn on the image. Button 132 n refreshes theimage by saving the line data but removing the display of drawn linesfrom the image. Button 132 o is clicked to confirm the tangent made fromseveral samples and icon 132 p is used when a single tangent is drawn.Button 132 q is an icon that brings up a help screen with one or moremenu choices to assist the user.

The user, after activating toolbar button 132 d, is prompted byapplication software 72 to scale a portion of or the entire x-axis 120 xof scanned ECG wave 120 by drawing a line generally parallel to x-axis120 x. The user is prompted by application software 72 to first clickmouse 68 at a selected first point, such as, for example, the origin, ofscanned ECG wave 120 and then at a second point spaced in the generaldirection of x-axis 120 x from the first selected point. Applicationsoftware 72 then prompts the user to enter a time interval or durationthat corresponds to the length of the line drawn. The requested timeinterval is entered by the user via either keyboard 66 or by selectingthe appropriate number from a pop-up list via mouse 68. Thus, theportion of x-axis 120 x of ECG wave 120 corresponding to the line drawnin the general direction of x-axis 120 x is assigned a time parameter orscale by application software 72. Alternatively, application software 72is configured with a default time scale, such as, for example 200 mS,and the user is instructed to draw a line generally parallel with x-axis120 x and extending through a portion of scanned ECG wave 120 thatcorresponds to the default time scale. In either embodiment, once a timescale has been assigned to at least a portion of x-axis 120 x of scannedECG wave 60, application software 72 then accordingly scales the entirex-axis 120 x of scanned ECG wave 120.

Y-axis 120 y or voltage axis is similarly provided with a scale. Theuser again accesses tool bar 130 of application software 72, which isdisplayed on display 70. By operating the preferred input device, button132 f is activated to enable the user assign a scale to y-axis 120 y ofscanned ECG wave 120. After activating toolbar button 132 f, the user isprompted by application software 72 to scale a portion of or the entirey-axis 120 y of scanned ECG wave 120 by drawing a line generallyparallel with y-axis 120 y by clicking the mouse at a first selectedpoint, such as, for example, the origin, of scanned ECG wave 120 andthen at a second point spaced from the first selected point in thegeneral direction of y-axis 120 y. Application software 72 then promptsthe user, in a manner similar to that described above for scaling x-axis120 x, to enter a voltage interval corresponding to the length of theline drawn. Thus, the portion of y-axis 120 y of ECG wave 120corresponding to the line drawn generally parallel to y-axis 120 y isassigned a voltage parameter or scale. Alternatively, applicationsoftware 72 is configured with a default voltage scale, such as, forexample 1 milliVolt (mV), and the user is instructed to draw a line thatis generally parallel to y-axis 120 y and which extends through aportion of scanned ECG wave 120 that corresponds to the default voltagescale. In either embodiment, once a voltage scale has been assigned toat least a portion of y-axis 120 y of scanned ECG wave 120, applicationsoftware 72 then accordingly scales the entire y-axis 120 y of scannedECG wave 120.

After the image is scaled, any horizontal or vertical distance betweentwo points is precisely measured without having to adjust the line to bea horizontal projection of the two points. The program next provides fortaking three RR intervals measurements 108, followed by three QTmeasurements 110 and finally the PR and QRS intervals. Since the RR andQT intervals are highly variable, it is conventional to take three ormore measurements and then take an average of them. The PR and QRSintervals are less variable and one measurement is usually sufficientfor ordinary diagnostic purposes.

Application software 72 further provides for the identification and/orlabeling of the characteristics of scanned ECG wave 120, and subsequentanalysis of the characteristics and parameters of scanned ECG wave 120.More particularly, the characteristics of scanned ECG wave 120, such as,for example, a QRS interval, an RR interval, a QT interval, or otherdesired characteristics and/or intervals, are identified by selecting adesired portion of scanned ECG wave 120 in RR interval identifying step108, QT interval identifying step 110, and PR/QRS interval identifyingstep 112.

In RR interval identifying step 108, QT interval identifying step 110and PR/QRS interval identifying step 112 (collectively referred tohereinafter as identifying steps 108-112), the user selects a desiredportion of scanned ECG wave 120 to be identified by clicking oractivating a button of mouse 68 at the beginning of the characteristicor interval to be identified and/or labeled. A first click sets one endpoint of a line, e.g. at the first R peak 24. The user holds the mousebutton down and drags mouse 68 to the end of the interval orcharacteristic of interest, e.g. the second R peak 34. As the user dragsmouse 68, application software 72 highlights the portion of scanned ECGwave 120 thus far selected. The user drags mouse 68 to the end of thedesired characteristic of interest, and releases the mouse button. Uponrelease of the mouse button, application software 72 activates pop-upmenu 122 (FIG. 6), which includes a list of typical characteristics fromwhich the user selects via mouse 68 or keyboard 66 the item thatcorresponds to the portion of scanned ECG wave 120 previously selected.Thus, the selected portion of scanned ECG wave 120 is labeled and/oridentified. In the example given above, the user has selected the firstof three RR intervals.

It is typical when analyzing an ECG plot to measure a maximum of threeRR intervals and three associated QT intervals. Furthermore, it istypical to measure a single PR and a single QRS interval. Thus,identifying steps 108-112 of application software 72 include defaultsettings which correspond to the typical intervals and the typicalquantities thereof. However, through a separate set of user accessiblemenus, the default settings of application software 72 are changed bythe user.

In addition to identifying and/or labeling characteristics of scannedECG wave 120 by selecting an interval thereof that corresponds to thedesired characteristic in identifying steps 108-112, applicationsoftware 72 enables a user to perform various additional measurementand/or identifying functions and techniques. Such additional techniquesare useful in identifying and/or measuring characteristics of an ECGplot that require baseline identification.

The baseline of an ECG plot, also referred to as the isoelectric line,is theoretically the zero volt line or level. However, the baseline ofan actual non-theoretical ECG plot does not necessarily correspond toand is typically not coincident with the actual zero volt line. Thus, itis often necessary to estimate the baseline of an ECG plot. The baselineis typically estimated as the line between two consecutive isoelectricpoints inside a PR interval of the EGG plot. During a PR interval themyocardium is generally assumed to be electrically neutral, and thus thetwo consecutive points are chosen to be within a PR interval.

Baseline identification is critical to the identification andmeasurement of various parameters of an ECG plot, such as, for example,QT intervals. Generally, the end of a QT interval is defined as thereturn of the T wave to the baseline of the ECG signal. Thus, in orderto properly measure and identify a QT interval, the baseline of the ECGplot must be identified. Conventionally, measuring and/or identifying aQT interval has been performed by what is referred to as the tangentapproach. Generally, the tangent approach involves establishing abaseline for the ECG plot, drawing a tangent line that is tangential tothe negative sloped or decreasing portion of the T wave, and drawing aline that indicates the onset of a QRS interval with which the T wave isassociated. The distance between the QRS onset and the point at whichthe tangent line intersects the baseline determines the QT interval.

When performed manually and directly on paper ECG plots, the tangentapproach is rather tedious and time consuming. Further, mistakes in themanual practice of the tangent approach are likely to require numerouserasures and thereby create a confusing ECG plot subject tointerpretational errors. The method of the present invention enables auser to quickly and easily practice the tangent approach and measure aQT interval by facilitating the identification of the ECG plot baseline,the drawing of tangent lines, and the indication of the onset ofassociated QRS intervals as more particularly described hereinafter.

Application software 72 enables a user to measure a QT interval bypracticing the tangent approach in a manner that substantially reducesthe problems associated with the manual performance thereof upon a paperECG plot. In order to do so, the user first selects from menu 122 ofapplication software 72 the appropriate Tangent option (i.e., Tangent 1,Tangent 2 or Tangent 3). More particularly, and with reference to FIG.7, the user selects from menu 122 the Baseline option and draws onscanned ECG plot 120 a single baseline 136 according to a click and dragmethod that is substantially similar to the method described above inregard to calibrating step 106 (i.e., the scaling of x and y axes 120 x,120 y, respectively), whereby the user clicks a button of mouse 68 overa starting point for baseline 136 and then drags mouse 68 to andreleases the mouse button at an ending point for baseline 136. Thebaseline 136 is constructed with one end point at a first QT region andthe second end point at the second or third QT region.

With baseline 136 thus established, the user selects from menu 122 ofapplication software 72 the appropriate Tangent option and draws atangent line. The tangent line is tangent to a selected or desirednegative-sloped portion of the T wave associated with the QT interval tobe measured. The method by which the tangent line is drawn issubstantially similar to the method described above in regard tocalibrating step 106, whereby the user clicks a button of mouse 68 on astarting point for tangent line and then drags mouse 68 to and releasesthe mouse button at an ending point for tangent line. Tangent line 150is thus drawn and appears on computer display 70. Tangent line 150 maybe rotated about either end point and may be transversely moved to otherparallel locations in order to precisely position the tangent line onthe declining T slope, as will be more particularly describedhereinafter.

Similarly, the QRS onsets of scanned ECG plot 120 are identified by theuser selecting from menu 122 of application software 72 the appropriateQonset command, i.e., Qonset 1, Qonset 2, or Qonset 3, which permit theuser to identify the onset of a QRS interval. After selecting thisoption, the user is prompted to position mouse 68 over the beginning ofa Q wave and click a mouse button to thereby establish the onset of aQRS interval. Application software 72 then generates and displays Q line160 which corresponds to the onset of a QRS interval associated with theselected Q wave.

QT intervals are calculated by the user activating button 132 p oftoolbar 130 by appropriate input via either keyboard 66 or mouse 68.Application software 72 calculates the distance between the intersectionof Q line 160 with baseline 136, which point is designated asintersection point 164 a in FIG. 7, and the intersection of tangent line150 with baseline 136, which point is designated as intersection point164 b in FIG. 7. This distance corresponds to the QT interval.

Each of tangent line 150 and Q line 160 include respective translationaltools 170 a, 170 b and 180 a, 180 b, graphically represented on scannedECG plot 120 as square boxes disposed at the end of tangent line 150 andQ line 160. Further, tangent line 150 includes rotational tool 190,which is represented on scanned ECG plot 120 as a round box near themidpoint of tangent line 150. Application software 72 enables a user toselect one of translational tools 170 a, 170 b and 180 a, 180 b totranslate, i.e., position relative to x-axis 120 x, a correspondingtangent line 150 and Q line 160, respectively. Similarly, applicationsoftware 72 enables a user to select rotational tool 190 to rotate,i.e., in a clockwise or counter-clockwise direction, tangent line 150.Thus, the user of application software 72 is able to easily and quicklymanipulate the horizontal position and angle of tangent lines and thehorizontal position of Q lines in order to identify and measure QTintervals in a more efficient and less error prone manner than whenmanually performing the tangent method on a paper ECG plot.

Alternatively, application software 72 is configured to perform thetangent method by establishing a separate baseline for each respectiveQT interval to be measured. This embodiment is particularly useful whenthe scanned ECG chart which is to be analyzed has a poorly-defined ordifficult to determine overall baseline. According to this embodiment, auser selects from a menu of application software 72 an option todetermine individual baselines, rather than the default singularbaseline (as described above), for each QT interval. Then, the processof establishing baseline 136, as described above, is repeated to therebyestablish a respective baseline for each QT interval to be measured.

In addition to the analysis and measurements described above, additionalmeasurements and parameters of scanned ECG plot 120, such as, forexample, average RR intervals, an average QT interval of the measured QTintervals, the QT interval corrected by the Bazett formula, and the QTinterval as corrected by the Fridericia formula, are automaticallydetermined by application software 72 performing the method of thepresent invention. As shown in FIG. 8, these quantities are displayed indialog box 200, which displays on display 70 a list of theaforementioned and other measurements and parameters of interest.

Application software 72 includes exporting step 118, which exports andsaves in a file the measured, calculated and qualitative parameters ofthe analyzed ECG wave on a selected one or both of storage device 74 andRAM 78. Referring now to FIG. 9, file 220 contains the parameters andmeasurements shown in FIG. 7, and is of a standard and widely-used fileformat, such as, for example, the American Standard Code for InformationInterchange (ASCII) file format. File 220 includes a list of parametersor measurement names, such as QRS, and a value associated with each ofthe parameters. However, it is to be understood that file 220 can bealternately configured, such as, for example, as a text file or otherfile format. Furthermore, it is to be understood that the data containedin file 220 can be alternately arranged, such as, for example, organizedinto a form that resembles typical sheets used in clinical trials or ina clinical report form format. Still further, file 220 can bealternately configured to include additional parameters andmeasurements, and to include qualitative parameters based upon theinterpretation of scanned ECG plot 120, such as, for example, commentson the quality of the ECG chart, indications of morphologies, etc.Moreover, file 220 can be alternately configured in a format compatiblefor use with any number of commercially available spreadsheet programsto thereby enable a user to graph, sort and perform further analysis ofthe data contained therein.

Alternatively, file 220 is configured in an application-specific formatreadable by application software 72, and includes a representation ofthe analyzed ECG wave, such as, for example, in a bitmap format thatincludes the wave itself, and data corresponding to any tangent lines, Qlines, QRS intervals, etc. Furthermore, file 220 alternatively includes,in addition to the representation of the analyzed ECG wave, the measuredand/or calculated parameters.

In the embodiments shown, the method of the present invention isdescribed in connection with the measurement and analysis of an ECGplot. However, it is to be understood that the method of the presentinvention can be applied to other types of electrophysiologic signals,plots, graphs, etc.

In the embodiment shown, scanning step 102 is controlled by operatingsystem 80 of computer 62. However, it is to be understood thatapplication software 72 can be alternately configured, such as, forexample, to control scanner 64 and perform scanning step 102.Furthermore, it is to be understood that application software 72 can bealternately configured to read and digitize output data directly from anEKG machine and display a scanned representation of the EKG machineoutput data, rather than scanning a paper ECG chart.

While this invention has been described as having a preferred design,the present invention can be further modified within the spirit andscope of this disclosure. This application is therefore intended tocover any variations, uses, or adaptations of the present inventionusing the general principles disclosed herein. Further, this applicationis intended to cover such departures from the present disclosure as comewithin the known or customary practice in the art to which thisinvention pertains and which fall within the limits of the appendedclaims.

What is claimed:
 1. A computerized method of analyzing anelectrocardiogram (ECG) paper chaff, comprising the steps of: scanningthe EGG chart to thereby create a computer-readable EGG image filerepresentative of the EGG chart; storing said EGG image file in a memoryof a computer; opening said EGG image file; displaying an EGG plot ofsaid ECG image file on a display of the computer; calibrating an x-axisand a y-axis of said EGG plot; identifying one or more features on saidEGG plot by using at least one input device connected to the computer;drawing a feature line with a first end point at one feature and secondend point at a second feature; and automatically finding the distancebetween the two end points as projected upon one or both fixes of saidEGG plot.
 2. The method of claim 1, wherein said scanning step comprisesscanning the ECG chart with an optical scanner.
 3. The method of claim1, wherein said storing step comprises storing said ECG image file in amemory of the computer, said memory comprising one of a random accessmemory, a read only memory, a hard disk and a floppy disk.
 4. The methodof claim 1, wherein said calibrating step comprises: scaling the x-axisof said ECG plot; and scaling the y-axis of said ECG plot.
 5. The methodof claim 4, wherein each of said scaling steps comprise: accessing atool bar displayed on the computer display; selecting a button of saidtoolbar corresponding to one of the x-axis and the y-axis of said EGGplot to thereby select one of the x-axis and y-axis for calibration; anddrawing a calibration line for one or both axes and assigning acalibrated scale to the length of the line and to the axes.
 6. Themethod of claim 5, wherein said drawing step comprises: drawing acalibration line of a predetermined length, said predetermined lengthcorresponding to a default value; and assigning said default value to aportion of the selected one of the x-axis and the y-axis, said portionhaving a portion length equal to said predetermined length.
 7. Themethod of claim 6, comprising the further step of calculating amagnitude of a projection of said feature line onto one of thecalibrated axes, said projection being substantially parallel to theselected axis, said magnitude corresponding to the product of the scaleof the axis and the length of the projected line.
 8. The method of claim5, further comprising the step of inputting a value corresponding to aprojection of said calibration line, said projection being substantiallyparallel to the selected one of the x-axis and the y-axis, said valuebeing assigned to an equal length of the selected one of the x-axis andthe y-axis.
 9. The method of claim 1, wherein said identifying stepcomprises selecting with an input device at least one of an RR interval,a QT interval, a PR interval, a QRS interval, a baseline, a tangentline, and an onset of a QRS interval.
 10. The method of claim 9, whereinsaid identifying step further comprises selecting a first point on theECG plot that corresponds to a beginning of a selected one of an RRinterval, a QT interval, a PR interval, a QRS interval, a baseline, atangent line, and an onset of a QRS interval, and selecting with aninput device a second point on the ECG plot that corresponds to an endof the selected one of an RR interval, a QT interval, a PR interval aQRS interval, a baseline, a tangent line, and an onset of a QRSinterval.
 11. The method of claim 10, further comprising the step oflabeling the selected one of an RR interval, a QT interval and a QRSinterval, a baseline and a tangent line.
 12. The method of claim 11,wherein said labeling step comprises selecting with an input device alabel from a menu displayed on the display of the computer, said labelcorresponding to the selected one of an RR interval, a QT interval, a PRinterval, a QRS interval, a baseline, a tangent line, and an onset of aQRS interval.
 13. The method of claim 1, wherein said measuring stepcomprises calculating a duration of at least one of an RR interval, a QTinterval, a PR interval and a QRS interval identified in saididentifying step.
 14. The method of claim 1, comprising the further stepof calculating and displaying a baseline of said ECG plot.
 15. Themethod of claim 14, wherein said calculating and displaying a baselinestep is performed separately for each QRS interval of the ECG plot tothereby establish a respective baseline for each QRS interval.
 16. Themethod of claim 1, comprising the further step of calculating with thetangent method a QT interval identified in said identifying step. 17.The method of claim 16, wherein said calculating with the tangent methodstep comprises: accessing a tool bar displayed on the computer display;selecting a button of said toolbar corresponding to said calculatingwith the tangent method step; and displaying on the display thecalculated QT interval.
 18. The method of claim 17, wherein each of saidcalculating an average of the RR intervals and said calculating anaverage QT interval comprises selecting a corresponding command form adialog box displayed on the display.
 19. The method of claim 18, whereinsaid exporting step further comprises storing data representative of theECG plot in said data file, storing data representative of saidcalibrating step, and storing data representative off said identifyingstep, to thereby enable subsequent display and analysis of the analyzedECG plot.
 20. The method of claim 1, comprising the further steps of:calculating an average of the RR intervals identified in saididentifying step and measured in said measuring step; and calculating anaverage QT interval of the QT intervals identified in said identifyingstep and measured in said measuring step.
 21. The method of claim 1,comprising the further step of: exporting the results of said measuringstep to a computer-readable file.
 22. A computerized method of analyzingan electrocardiogram (ECG) paper chart, comprising the steps of:scanning the ECG chart to thereby create a computer-readable ECG imagefile representative of the ECG chart; storing said ECG image file in amemory of a computer; opening said ECG image file; displaying an ECGplot of said ECG image file on a display of the computer; scaling eachof an x-axis and a y-axis of said ECG plot by accessing a toll bardisplayed on the computer display, selecting a button of said toolbarcorresponding to one of the x-axis and the y-axis to thereby select oneof the x-axis and y-axis for calibration, and drawing a line generallyparallel with the selected one of the x-axis and the y-axis of said ECGplot; identifying characteristics of said ECG plot by selecting with aninput device connected to the computer at least one of an RR interval, aQT interval, a PR interval, a QRS interval, a baseline, a tangent line,and an onset of a QRS interval; and drawing a feature line between twofeature points and finding a projected axial distance between the twofeature points by calculating a duration each of the RR intervals, QTintervals, PR intervals and QRS intervals identified in said identifyingstep.
 23. The system of claim 22, wherein said application softwareincludes: a scanning module enabling a user to control said scanner toscan the ECG chart and thereby create a computer-readable ECG image filerepresentative of the ECG chart; a storing module saving said ECG imagefile in a memory of a computer; a file open module to enable a user toopen said ECG image file; a display module displaying an ECG plot ofsaid ECG image file on a display of the computer; a calibrating moduleto calibrate an x-axis and a y-axis of said ECG plot; an identifyingmodule to identify characteristics of said ECG plot by using at leastone input device connected to the computer; a measuring module measuringsaid identified characteristics; and a calculating module calculatingparameters of said ECG plot based upon said identified characteristics.24. A system for analyzing an EGG paper chart, comprising: a computerhaving a display, keyboard and mouse; a scanner electricallyinterconnected with said computer; and application software stored in amemory of said computer and being executable thereon, said applicationsoftware configured for displaying, identifying, measuring andcalculating characteristics of an image file representing said EGGchart, and drawing a feature line between two characteristics, saidimage file created by scanning with said scanner the ECG chart.